Detailed experimental data are presented on the transition between regular and Mach reflexion. Data have been obtained for steady, pseudo-steady and un-steady flows, and include a study of the continuous and discontinuous transitions predicted by previous researchers. It is found that the criterion often used to calculate the transition condition is wrong in every case that we have investigated. In its place we propose an alternative criterion which has the property that the system remains always in mechanical equilibrium during transition.

Our 1975 paper reported the results of experiments on shock reflexion in a wind tunnel and a shock tube; further results are presented here. For strong shocks it is shown that transition to Mach reflexion takes place continuously at the shock wave incidence angle ω0 corresponding to the normal shock point ω0 = ωN, unless the downstream boundaries form a throat. In this event transition can be promoted anywhere within the range ω0 [les ] ωN, and it is even possible to suppress regular reflexion altogether! However when ω0 < ωN the transition is discontinuous and accompanied by hysteresis. Again for strong shocks evidence is presented which suggests that the famous persistence of regular reflexion beyond the ωN point ω0 > ωN is spurious. For weak shocks the transition condition is not known but it is found that even for regular reflexion a marked discrepancy between theory and experiment develops as the shocks become progressively weaker. Also when weak shocks diffract over single concave corners there is a somewhat surprising discontinuity in the regular reflexion range. It seems that none of these phenomena can be adequately explained by real gas effects such as viscosity and variation of specific heats.

This paper presents experimental data obtained for the refraction of a plane shock wave at a carbon dioxide–helium interface. The gases were separated initially by a delicate polymer membrane. Both regular and irregular wave systems were studied, and a feature of the latter system was the appearance of bound and free precursor shocks. Agreement between theory and experiment is good for regular systems, but for irregular ones it is sometimes necessary to take into account the effect of the membrane inertia to obtain good agreement. The basis for the analysis of irregular systems is one-dimensional piston theory and Snell's law.

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This paper reports on an experimental investigation aimed at reducing the injury associated with head-on collisions between passenger vehicles and trucks, or other heavy vehicles.Full-scale truck-to-car crash tests were performed using a prototype energy absorbing underride-resisting bumper bar system, at impact speeds ranging from 56 to 100 km/h. The system consists of a rigid barrier attached to the chassis by four telescopic struts incorporating ball joints at each end, making the assembly a pin-jointed mechanism. Energy absorption is via the plastic deformation of thinwall steel tubing undergoing inversion and buckling. The properties of the steel tubes were determined in quasi-static and dynamic tests at 30 km/h and 80 km/h. No strain rate sensitivity was detected in these tests. The results were therefore used to estimate the energy absorbed by the truck bumper bar system under full-scale test collisions.From these initial tests it can be concluded that with suitable energy absorbing and underride-resisting truck bumper bars it is possible to significantly reduce the severity of head-on collisions.